Field of the Invention
The present invention relates to optical fibers and light source devices.
Description of the Related Art
When high-intensity light, such as short-pulse light with the pulse width of picoseconds or femtoseconds, pulse light with the pulse width of about nanoseconds, or continuous light, propagates through a nonlinear medium, such as an optical fiber, it is known that broadband light is generated in accordance with a nonlinear optical phenomenon occurring in the nonlinear medium. The broadband light obtained in accordance with this phenomenon is called supercontinuum (SC) light. Because SC light has properties such as broadband, high power, and flat spectrum, it is expected that such SC light is to be applied to, for example, optical measurement or near-infrared spectroscopy.
W. J. Wadsworth, et al., “Supercontinuum and four-wave mixing with Q-switched pulses in endlessly single-mode photonic crystal fibres” OPTICS EXPRESS, Vol. 12, No. 2, pp. 299-309 describes a result in which SC light is generated by using a photonic crystal fiber (PCF) as an optical fiber that causes a nonlinear optical phenomenon to occur. However, a PCF has a special structure with a plurality of holes extending in the axial direction within the cross section of the fiber, and is problematic in that the manufacturing cost thereof is high.
Thus, there have been many reports describing that SC light is generated by using a highly-nonlinear optical fiber that uses silica glass as a base, the highly-nonlinear optical fiber having a core with a high refractive index and a cladding with a low refractive index (for example, see JP 2007-279704 A (referred to as “Patent Literature 1” hereinafter) and JP 2010-49089 A (referred to as “Patent Literature 2” hereinafter). These highly-nonlinear optical fibers have a simple solid structure without any holes. However, in the technology in the related art that uses highly-nonlinear optical fibers, it is difficult to expand the SC-light band to a long wavelength of 2400 nm or longer and to a short wavelength of 850 nm or shorter.